Two-pole impedance sensors for biosensor technology are known from the prior art, see e.g. [1] to [8]. Furthermore, two-pole impedance methods have also been proposed for the sensor technology of other chemical substances, e.g. in the context of gas sensor technology.
Reference [9] discloses CMOS sensor interface arrays for DNA detection.
A description is given below referring to FIG. 1A, FIG. 1B, of a sensor arrangement 100 in accordance with the prior art.
FIG. 1A shows a plan view of the sensor arrangement 100, which is integrated in a silicon substrate 103. A first interdigital electrode 101 is provided in a first surface region of the silicon substrate 103. A second interdigital electrode 102 is provided in another surface region of the silicon substrate 103. The interdigital electrodes 102, 103 are configured in interdigitated fashion.
FIG. 1B shows a cross sectional view 110 of the sensor arrangement 100 along a sectional line A-A′.
The sensor arrangement 100 known from [4], [7], [8] can be used for carrying out a two-pole impedance measurement in the context of DNA sensor technology. The sensor electrode 100 contains two interdigital electrodes 101, 102 comprising fingers arranged periodically next to one another in one dimension.
Furthermore, FIG. 1B shows a partial region 110 of the sensor arrangement 100, which partial region is described in more detail below on the basis of FIG. 2A, FIG. 2B in order to elucidate the principle and the functioning of the sensor arrangement 100.
FIG. 2A shows the partial region 111 of the sensor arrangement 100 in a first operating state, in which an analyte having particles to be detected has not been brought into contact with the sensor arrangement 100. Catcher molecules 200, e.g. DNA single strands, are immobilized on the electrodes 101, 102. Gold is often used as material for the interdigital electrodes 101, 102, so that the catcher molecules 200 are immobilized by means of the gold-sulfer coupling—frequently used in biochemistry—between gold material of the interdigital electrodes 101, 102, on the one hand, and thiol groups (SH groups) of the catcher molecules 200 on the other hand.
FIG. 2B shows a second operating state of the sensor arrangement 100 after the latter has been brought into contact with an analyte having particles 202 to be detected. Consequently, the analyte to be examined, which comprises an electrolyte possibly having particles 202 to be detected, is situated above the sensor electrodes 101, 102 during active sensor operation. A hybridization, as is illustrated schematically in FIG. 2B, that is to say a bonding of DNA single strands 202 to the catcher molecules 200, takes place only when catcher molecules 200 and DNA single strands 202 match one another in accordance with the key-lock principle, which is referred to as a “match”. If this is not the case, then hybridization is not effected. This situation is referred to as a “mismatch”. The specificity of the sensor is thus derived from the specificity of the catcher molecules.
The electrical parameter evaluated in accordance with the sensor principle of the sensor in accordance with FIG. 2A, FIG. 2B is the impedance 201 between the electrodes 101, 102, which are shown schematically in FIG. 2A, FIG. 2B. In the case of a hybridization that has taken place (if appropriate after a rinsing step following the hybridization phase), the vale of the impedance 201 changes since DNA molecules 202 and catcher molecules 200 have different electrical properties than the electrolyte, and since electrolyte material is displaced from the region between the electrodes 101, 102 during the hybridization.
A description is given below, referring to FIG. 3, of a different partial view 300 of the sensor arrangement 100 from FIG. 1B, in which electrical field lines 301 between the electrodes 101, 102 are depicted schematically. The electrical field line profiles 301 of the interdigital structures 101, 102 have, as shown in FIG. 3, lines of symmetry 302 which can be used for the analytical description and assessment of the properties of the sensor arrangement.
However, the sensor arrangements based on interdigital electrodes known from the prior art, such as the sensor arrangement shown in FIG. 1A to FIG. 3, do not have a sufficient detection sensitivity for many applications.